1. Field of the Invention
The present invention relates to communications; more specifically, communications in a multi-service provider environment.
2. Description of the Related Art
FIG. 1 illustrates a portion of the radio frequency spectrum. Frequency range 10 centered around 800 MHz has historically been known as the cellular frequency range and frequency range 12 centered about 1900 MHz is a newer defined frequency range associated with personal communication services (PCS). Each range of frequencies, i.e., the cellular and PCS, are broken into two portions. In cellular frequency range 10, there is uplink portion 13 which is used for communications from a mobile communication device to a base station such as a cellular base station. Portion 16 of cellular frequency range 10 is used for downlink communications, that is, communications from a cellular base station to a mobile communication device. In a similar fashion, Portion 18 of PCS frequency range 12 is used for uplink communications, that is, communications from a mobile communication device to a base station. Portion 20 of PCS frequency range 12 is used for downlink communications, i.e., communications from a base station to a mobile communication device.
Each of the frequency ranges are broken into bands which are typically associated with different service providers. In the case of cellular frequency range 10, frequency bands 30 and 32 are designated band xe2x80x9caxe2x80x9d for uplink and downlink communications, respectively. In a particular geographic area, a cellular service provider is assigned frequency band xe2x80x9caxe2x80x9d in order to carry out mobile communications. Likewise, in the same geographic area another cellular service provider is assigned frequency bands 34 (uplink) and 36 (downlink) which are designated band xe2x80x9cbxe2x80x9d. The frequency spectrums assigned to the service providers are separated so as to not interfere with each other""s communications and thereby enable two separate service providers to provide service in the same geographic area. Recently, the U.S. Government auctioned the PCS frequency spectrum to service providers. As with the cellular frequency range, the PCS frequency range is broken into several bands where a different service provider may use a particular frequency band for which it is licensed within a particular geographical area. The PCS bands are referred to as A, B, C, D, E and F. The A band includes uplink band 50 and downlink band 52. The B band includes uplink band 54 and downlink band 56. Band C includes uplink band 58 and downlink band 60. Each uplink and downlink band of the A, B and C bands are approximately 30 MHz wide. The D band includes uplink band 62 and downlink band 64. The E band includes uplink band 66 and downlink band 68. Likewise, band F includes uplink band 70 and downlink band 72. The uplink and downlink bands of bands D, E and F are approximately 10 MHz wide each. It should be noted that with the cellular and PCS frequency bands, it is possible to have as many as eight different wireless communication service providers in a particular area.
Each of the different cellular and PCS bands consist of control channels and communication channels in both the uplink and downlink direction. In the case of analog cellular bands, there are 21 control channels for both the xe2x80x9caxe2x80x9d, and xe2x80x9cbxe2x80x9d bands. Each of the control channels include an uplink and a downlink portion. The control channels transmit information such as an SOC (System Operator Code), an SID (System Identifier Code), paging information call setup information and other overhead information such as information relating to registering with the mobile communication system. The portion of the cellular band""s spectrum not occupied by the control channels is used for communication channels. Communication channels carry voice or data communications, where each channel consists of an uplink and downlink communications link. Presently there are several cellular communication standards. An analog standard known as EIA/TIA 553 was built upon the AMPS (Advanced Mobile Phone Service) standard. This standard supports 21 analog control channels (ACC) and several hundred analog voice or traffic channels (AVC). A newer standard is the EIA/TIA IS54B standard which supports dual mode operation. Dual mode operation refers to having an analog control channel, and either an analog voice/traffic channel or a digital traffic channel (DTC). The AVC or DTC are used for actual communications, and the ACC is used to transfer information relating to, for example, call set-ups, service provider identification, and the other overhead or system information.
A newer standard, the EIA/TIA IS136 standard supports communications covered by both analog and dual mode cellular, and also includes a totally digital communication scheme which was designed for the PCS frequency bands A-F and cellular frequency bands xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d. This standard allows for a digital traffic channel (DTC) and a digital control channel (DCCH). In the case of the DTC, not only is the voice or data communicated, but in addition, a digital channel locator (DL) is transmitted in the DTC. The DL enables a mobile communication device that locks onto the DTC to use the information in the DL to locate a DCCH for purposes of obtaining information such as the SOC, SID, paging information, and other system overhead information carried on the digital control channel.
When a mobile communication device such as a mobile telephone attempts to register with the service provider, it locks onto a control channel and reads information such as the SOC and SID. If the SOC and/or SID correspond to a service provider with which the user has a communication services agreement, the telephone may register with the service provider""s mobile communication system via the up-link control channel.
FIG. 2 illustrates a map of the United States illustrating cities such as Seattle, Chicago and Washington, DC. For example, in Seattle frequency band A has been licensed to SOC (Service Operator Code) 001 with a SID of 43 and band C has been licensed to SOC 003 with a SID of 37. In Chicago, suppose that frequency band C has been licensed to SOC 001 with a SID equal to 57, and that band B has been licensed to SOC 003 with a SID of 51. In Washington, DC suppose that frequency band xe2x80x9caxe2x80x9d has been licensed to a SOC 001 with a SID of 21, and that band A has been licensed to SOC 003 with a SID of 17. It should be noted that the same SOC may be found in several different locations although on different frequency bands. It should also be noted that the same SOC will be associated with different SIDs in each geographical area and that in the same geographic area different service providers have different SIDs. If a particular subscriber to a wireless telecommunication service has an agreement with a service provider having a SOC of 001, that subscriber would prefer to use systems with a SOC of 001 because the subscriber is likely to receive a less expensive rate. When the subscriber is in Seattle he/she would prefer to be on band A, and if in Chicago on band C, and if in Washington, DC on band xe2x80x9caxe2x80x9d. The above described situation presents a problem for a wireless communication service subscriber. As a subscriber moves from one area of the country to another, the telephone when turned on, searches for the xe2x80x9chomexe2x80x9d service provider, or the service provider with which the subscriber has a pre-arranged agreement. If for example, the subscriber travels from Seattle to Chicago, when turning the phone on in Chicago, the phone will search through the different bands of the spectrum to identify the service operator with the code 001 in order to find the desired service provider.
In order to find a particular service provider, the phone may have to search through both the xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d cellular bands, and through the eight PCS bands. It should be recalled that there are up to 21 different ACCs in each of the xe2x80x9caxe2x80x9d and xe2x80x9cbxe2x80x9d cellular bands. It may be necessary to check 42 ACCS in order to find an ACC from which a SOC or SID may be obtained. Additionally, searching for a particular SOC or SID in PCS bands A through F is particularly time consuming. The digital control channels (DCCHs), which contain the SOC and SID, are not assigned to specific frequencies within a particular PCS band. As a result, the mobile communication device may find it necessary to search through the spectrum of each PCS band looking for a DCCH, or an active DTC that has a digital channel locator (DL) which will direct the mobile communication device to the DCCH. As illustrated above, the process of searching for a particular service provider is laborious and may require a period of time on the order of several minutes.
An embodiment of the present invention provides a method for locating a particular or desirable communications service provider in an environment having a plurality of service providers. After power-up, a mobile communications device such as a cellular telephone, checks the most recently used control channel to determine whether an optimal service provider is available on that channel. If an optimal service provider is not available or if that channel is not available, the mobile communication device performs a search through frequency spectrum in a pre-determined order until an optimal or acceptable service provider is located.
In another embodiment of the invention, the frequency spectrum is searched in a pre-determined order that changes based on information entered by a mobile communication device distributor or mobile communication device user. In yet another embodiment of the invention, the pre-determined order for searching the spectrum for service providers is updated by over the air programming. In still another embodiment of the present invention, the pre-determined order for searching is based on the mobile communication device""s operational history.
In yet another embodiment of the invention, the communications device registers with a less preferred service provider in a first frequency band. While remaining registered with the less preferred service provider, the device examines several frequency bands in the order specified by the frequency band search schedule. A frequency band is examined by dividing the frequency band into many sub-bands, and by locating the strongest signal above a threshold within the sub-band being examined. The examination continues until a second frequency band having a more preferred service provider is located. The communication device then registers with the more preferred service provider.